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SECTION 7. STANDARD EXTENSIONS

Character fields  The value of a character-formatted (Aw) field is a character string

of width w containing the characters in columns TBCOLn through TBCOLn+w - 1. The

character string shall be composed of the restricted set of ASCII text characters with

decimal values in the range 32 through 126 (hexadecimal 20 through 7E).

Integer fields  The value of an integer-formatted (Iw) field is a signed decimal integer

contained in columns TBCOLn through TBCOLn+w - 1 consisting of a single optional sign

(`+' or `-') followed by one or more decimal digits (`0' through `9'). Non-significant

space characters may precede and/or follow the integer value within the field. A blank

field has value 0. All characters other than leading and trailing spaces, a contiguous

string of decimal digits, and a single leading sign character are forbidden.

Real fields  The value of a real-formatted field (Fw.d, Ew.d, Dw.d) is a real number

determined from the w characters from columns TBCOLn through TBCOLn+w - 1. The

value is formed by

1. discarding any trailing space characters in the field and right-justifying the re-

maining characters,

2. interpreting the first non-space characters as a numeric string consisting of a single

optional sign (`+' or `-') followed by one or more decimal digits (`0' through

`9') optionally containing a single decimal point (`.'). The numeric string is

terminated by the end of the right-justified field or by the occurrence of any

character other than a decimal point (`.') and the decimal integers (`0' through

`9'). If the string contains no explicit decimal point, then the implicit decimal

point is taken as immediately preceding the rightmost d digits of the string, with

leading zeros assumed if necessary. The use of implicit decimal points is deprecated

and is strongly discouraged because of the possibility that FITS reading programs

will misinterpret the data value. Therefore, real-formatted fields should always

contain an explicit decimal point.

3. If the numeric string is terminated by a

(a) `+' or `-', interpreting the following string as an exponent in the form of a

signed decimal integer, or

(b) `E', or `D', interpreting the following string as an exponent of the form E or

D followed by an optionally signed decimal integer constant.

4. The exponent string, if present, is terminated by the end of the right-justified

string.

5. Characters other than those specified above, including embedded space characters,

are forbidden.

FITS Standard